Temperature sensitive control circuit for internal combustion engines having a fuel injection system



Elited tates Patent Inventors 7 Appl. No.

Filed Patented Assignee Priority a Limited Liability Company of Germany May 24, 1968 Germany 1 ,75 1,41 0

TEMPERATURE SENSITIVE CONTROL CIRCUIT FOR INTERNAL COMBUSTION ENGINES HAVING A FUEL INJECTION SYSTEM 13 Claims, 3 Drawing Figs.

U.S. Cl... 123/32, I 123/ll9,123/139,123/l79 Int. Cl ,.F02m 51/00 Field ofSearch 123/32(E),

32(E)-l,32,119,139.17,l39.18,140.3,179(A), 179(8), 179(L), 179(6) References Cited Primary Examiner- Laurence M. Goodridge At10rney-Flynn and Frishauf ABSTRACT: A bridge circuit is connected across the engine battery, one branch of the bridge circuit including a temperature sensitive resistance such as a negative temperature coefficient resistance; the cross terminals of the bridge include the base-emitter path of a transistor in series with an oppositely poled diode, the emitter-collector path of the transistor controlling through a bistable flip-flop circuit an output transistor which has an electromagnetic operating coil, such as a relay, in series with its collector-emitter path to inject additional fuel into the intake manifold of the internal combustion engine when the negative temperature coefficient resistance has a value indicating low engine temperature, and thus causes imbalance of the bridge. The diode in series with the baseemitter path of the transistor compensates for ambient temperature changes'to which the control circuit may be exposed independent of engine operating temperature.

Patented Oct. 13, 1970 Sheet Z era 3 W M Fm T 4 w y F Patented Oct. 13, 1970 Sheet w r W J 2 m i h w w w T The present invention relates to a control system for internal combustion engine fuel injection systems which is highly temperature-sensitive, and more particularly to an arrangement which provides additional injected fuel if the engine temperature is low.

Electronically controlled fuel injection systems may be so arranged that the amount of fuel to be injected during any work cycle is dependent on the temperature, so that, at low temperatures, a greater amount of fuel is injected. If the temperatures are exceedingly low,-however, fuel gasifies only poorly and difficulties may arise particularly upon starting. It is therefore desirable to provide additional fuel as an assistance for starting when engines are exposed to unusually low temperatures.

It is an object of the present invention to provide a temperature-sensitive control circuit tocause injection of additional fuel upon starting at low temperatures;

Subject matter of the present invention: Briefly, an additional fuel injection valve is provided, located for example, in the intake manifold at a position where fuel injected therefrom is supplied to all cylinders of the engine supplied by t the particular manifold. The control circuit includes a bridge connected across the electrical supply of the vehicle, one branch of the bridge circuit being provided with a temperature-sensing resistance, such as a negative temperature coefficient resistor. The diagonal, or cross connection of the bridge is formed by the base-emitter path of an input transistor, connected in series with a diode (or the diode portion of some other semiconductor element); a biasing resistor is connected between the base and one of the battery terminals so that, upon imbalance of the bridge, the transistor changes conductivity to control the further fuel injection valve.

The diode, in series with the base-emitter path of the transistor, and connected as aforesaid, renders the control circuit, apart from the negative temperature coefficient resistor, essentially independent of ambient temperature, so that the negative temperature coefficient resistor can serve as the sole measuring element to govern the function of the control circuit. This resistor, if located in heat-conductive relation with respect to the engine, or the intake manifold thereof, may thus reflect an accurate measurement indication of the temperature at which the injected fuel is to be gasified independently of the temperature to which the remaining elements of the control circuit are exposed.

The invention will be described by way of example with reference to the accompanying drawings, wherein:

FIG. 1 is an abbreviated schematic diagram of a fuel injection arrangement for internal combustion engines with the additional starting injection control added thereto;

FIG. 2 is a circuit diagram of the additional control circuit for the injection of additional fuel; and

FIG. 3 is a graph of current flow through the control circuit of the additional fuel injection valve (i vs. temperature (T).

The internal combustion engine 10, illustrated as a fourcylinder engine, has four spark plugs llconnected to an ignition system, not shown. The four cylinders are each connected to an inletstubvwhich terminates in a common manifold 12. Each of the inlet stubs leading to the cylinders has a fuel injection valve 13 associated therewith. Fuel lines [4 supply fuel, under pressure, to the fuel valves 13. The fuel in lines 14 is obtained from a circulating line 15 where fuel from a tank 19, conducted over filter l6 and raised to a pressure of about 2 atgauge by means of a pump 18, driven by a motor 17 is connected; pressure regulator 20 is inserted in the line to keep the pressure constant; it is connected by means of return line 21 back to the tank. j

A throttle .25, controlled by an accelerator pedal 26, is interposed in the line between intake manifold 12 and an air filter 27. When the engine 10 is'operating, the pressure (or, rather, vacuum) within inlet manifold 12 will change in depen- .dence on the position of the throttle 25. If throttle 25 is completely open, intake manifold 12 will be at approximately ambient air pressure, which will depend on the elevation of the position of the engine above sea level. When throttle 25 is variables during operation of the internal combustion engine l0.

An electronic fuel injection control system, essentially ineluding a monostable multi vibrator circuit 28 and an amplifier 29, connected thereto, controls the distribution and the length of opening pulses to be applied to the fuel injection valves 13. The output of the'amplifier 29, selectively switched between a pair of output lines, is connected to the two left, and the two right injection valves, respectively, as pairs over equalizing resistances 30, 31. The control system is supplied with power from a battery, schematically indicated only by positive terminal i.

' A contact 36, driven by a cam 35 having two rises and connected to the cam shaft of the engine, as indicated by the chain-dotted line 34, controls the start of the pulses of multi vibrator 28. Each time when contact 36 closes, multi vibrator 28provides a pulse, amplified in amplifier 29, and alternately applied to the two left, and two right valves 13. The duration t, of the pulses obtained from the multi vibrator 28 is controlled by the pressure in inlet manifold 12. A transducer 37, connected to inlet manifold 12 by means of a line 38 provides an electrical quantity representative of the vacuum in manifold 12; line 39 schematically indicates the control connection from transducer 37 to the multi vibrator 28, and thus control of the pulse duration 1,. The duration of the pulse t, is so arranged that low vacuum (high air pressure) in intake manifold 12, and corresponding to open throttle 25 will result in a long pulse duration, for example 8milliseconds; if the vacuum in intake manifold 12 is high, corresponding to closed or almost closed throttle and small angle a, the pulse period t, will be short, for example 2 milliseconds. This pulse period can be made additionally dependent on various operating parameters, for example the speed of the engine, temperature of the engine during operation, battery voltage, and the like.

In accordance with the present invention, additional fuel is supplied to the engine to assist during cold weather starting. An additional fuel injection valve 44 is located in intake manifold 12 in the region of the bend of the manifold, that is at the point of distribution 'of inlet airto all the cylinders and where the intake manifold is still common to all cylinders and has not yet branched to the individual cylinder inlet stubs. The additional valve 44 is connected to fuel pressure line 15 by an additional fuel supply line 45. Operation of the valve 44 is controlled by the control system of the present invention, illustrated schematically as block 42 in FIG. 1 and shown in detail in FIG. 2. Control system 42 is separately connected to be effective only when starter switch 46 is operated. The control system 42 is governed by the resistance of a separate temperature sensitive resistor 41 located at a suitable position on the internal combustion engine at, or near its top, or close to the point at which the fuel is to gassify, that is close to the mantle of the engine in the region of the injection valves. One terminal of temperature sensitive resistor 41 which, for example, may be a negative temperature coefficient'resistance, is electrically connected to the chassis of the engine through the engine housing itself, the other terminal being connected to circuit 42. When installed in an automotive vehicle, the usual ignition switch (not shown) connects, or interrupts battery supply.

Referring now to FIG. 2: The negative terminal of a battery 50 is connected to chassis; a starter switch 46 connects the positive terminal of the battery to the starter relay schemati- .cally indicated at 51, in order to start the internal combustion engine 10. The other terminal of starter relay 51 is connected to chassis. Ignition switch 52, also connected to the positive terminal of battery 50, is connected to a positive line, or bus 53 which forms one terminal of the power supply for the fuel injection control system. A bridge network has one branch formed of a fixed resistance 54 and the negative temperature coefficient resistance 41, the other end of which is connected to chassis or ground. One cross connection, or diagonal point of the bridge is indicated by junction 60, connected to the anode of diode S; thecathode' of diode 55 is connected to the base of a pnp transistor 56 which is part of a bistable flip-flop circuit consisting additionally of a pair of npn transistors 66, 67. A biasing resistance 57 connects between the base of transistor 56 and chassis, and a condenser 58 between the base of transistor 56 and positive bus 53.

The other branch of the bridge network is formed by a potentiometer 62, a resistance 61, and another potentiometer or adjustable resistance 59. The other cross connection, or diagonal connection point of the bridge is indicated at 70. Adjustable resistance 62 is connected in series with another resistance 64 and forms, together with it, a voltage divider. The diagonal, or cross connecting circuit of the bridge is thus formed by the emitter-base path of transistor 56, in series with diode 55. I

The collector of transistor 56 is connected over a current limiting resistance 65 to the base of npn transistor 66, and also over a resistance 68 to chassis. Collector resistor 69 is connected between positive bus 53 and the collector of transistor 56; a diode interconnects the collector of transistor 66 with the base of npn output transistor 67, and is poled as shown, that is with the anode of diode 71 connected to the collector of transistor 66. A resistance 72, in series with a condenser 73 is connected further between the base of transistor 66 and the cathode of diode 71'.

A group of diodes 74, forming a constant voltage source, are connected between the base of output transistor 67 and chassis; additionally, the base of transistor 67 is connected by a resistance 75 to the emitter of transistor 67. The emitter 67 is additionally connected over a sensing resistance 76 to chassis. An electromagnetic operating element, illustrated as a relay coil 77 is connected between the collector of transistor 67 and the starter switch 46. The relay coil 77, itself, has a freewheeling diode 78, in series with a resistance 79 connected in shunt thereto, to provide a damping circuit and to suppress voltage peaks. A junction point 63, which is at collector potential of transistor 67 is further connected by means of a protective or second freewheeling diode 81 to chassis. The armature of relay coil 77 operates a switch 82 which is connected in series with an operating winding 83 to operate the additional fuel injection valve 44 to admit fuel to the intake manifold. Junction 63 interconnects with the voltage divider formed of resistances 62, 64.

Operation: To start the engine, ignition switch 52 is closed which provides operating potential for the control circuit. Upon operation of starter switch 46, the starting motor solenoid 51 will be energized and, additionally, electrical power will be made available to the relay coil 77. The bridge circuit formed of resistances 55, 41 and 62, 61, 59 will be connected across battery voltage. Initially, the function of resistance 64 and the voltage divider will be neglected. The voltage across the diagonal of the bridge, that is the circuit between junctions 60 and 70 and including diode 55 and the base-emitter junction of transistor 56 will thus be determined by the temperature of the negative temperature coefficient resistance 41, the value of which will depend on the temperature of engine 10. The values of the various resistances in the bridge circuit are so arranged that if the temperature of the engine is very low, the resistance of negative temperature coefficient 41 will be so high that the base of transistor 56 will be more positive than its emitter, to block transistor 56. Transistor 56, the base of which is connected over resistance 68 to chassis, likewise remains blocked. Transistor 69, however, has current flowing to the base to render it conductive.

Upon conduction of transistor 67, operating power from battery 50 is connected over starter switch 46 to relay coil 77 causing operation of switch 82 and energization of operating coil 83 of valve 44. Thus, when the temperature of the engine is very low, additional fuel is injected into the portion of the intake manifold 12 of engine 10 which is common to all the cylinders. The temperature at which the additional fuel injection system will respond can be changed by adjustment of resistances 62, and 59, respectively; injection of additional fuel into the intake manifold provides for reliable starting even at lowest temperatures. Relay 77, of course, is not strictly necessary and control of coil 83 can be obtained directly, if transistor 67 is of sufficient current carrying capacity; of course, alternatively, solid state switches can be used instead of the mechanical relay formed of coil 77 and contacts 82.

if the engine is already at a higher temperature when it should be started, for example after having been in operation, negative temperature coefficient resistance 41 will have a fairly low value. Upon connection of the ignition switch 52, the base of transistor 56 will then be more negative than the emitter, and transistor 56 will be conductive. Current will flow over resistances 62, 61, the emitter-collector path of transistor 56 and over the current limiting resistance 65 to the base of transistor 66 which, likewise, will become conductive and cause transistor 67 to turn off. With transistor 67 blocked, the coil of relay 77 will not operate even when starter switch 46 is closed and no additional fuel will be injected. Thus, additional fuel is supplied only to cold engines, and not to warm ones.

Negative temperature coefficient resistance 41 acts as a sensing resistance for the entire network 42. Network 42, however, itself should be independent of ambient temperature. Diode 55 largely compensates for temperature dependence of the knee of the characteristic curves of the baseemitter current of diode 56; in a preferred form, both diode 55 as well as transistor 56 are silicon semiconductor devices.

When the temperature is very low and diode 55 is conductive because resistance 41 has a high value, current will flow from positive bus 53 over resistance 54, diode 55 and then to ground over resistance 57. Junction is at a higher value, that is it is more positive than junction point 7 and transistor 56 is blocked. As the temperature of engine 10 increases, the resistance of resistor 41 gradually decreases, and an increasing portion of the current to junction 60 will flow through resistance 41, until diode 55 will block. Resistance 57 now will carry the base current in transistor 56, causing transistor 56 to become conductive. This will occur as soon as the base emitter voltage has a predetermined value, depending on the type of transistor, and for a silicon switching transistor usually in the range 0.6 V. This typical value is temperature dependent; if diode 55 is essentially of the same material, and is reversely poled with respect to the junction between base and emitter of transistor 56, the temperature dependence of the junction current from emitter to base is largely compensated. Diode 55 has the additional advantage that it prevents excess voltages on transistor 56. If the engine 10 reaches a high temperature, resistance 41 may reach a value which is so low that the base current through transistor 56 would become excessive, permanently damaging the transistor; diode 55, however,

is blocked under such operating conditions so that the base current of transistor 56 is solely determined by the value of the base biasing resistance 57.

In accordance with a feature of the invention, the branch of the bridge circuit from junction to positive bus 53 is not directly connected to the positive bus, but rather to the tap point of a voltage divider formed of resistances 62, 64. These resistances are connected in parallel with relay 77 during starting, which further improves the reliability of the switchover of the bistable circuit. [f transistor 56 is conductive, the output transistor 67 is blocked. No current will flow over resistance 64 and thus the emitter of transistor 56 will be more positive, since the voltage drop in resistances 62, 61 will be less, causing full conduction of transistor 56 to saturation value. Transistor 56 will only block when the voltage at diagonal junction point 60 of the bridge is positive by a value which is so much greater than the amount by which the emitter voltage of transistor 67 became more positive when transistor 67 blocked, The circuit will thus have a certain lag, or hysteresis. The distance between the change-over, or the delay is adjustable by changing the value of resistance 62. This lag, or hysteresis should be as great as possible in order to make the entire circuit independent of noise, or stray voltage peaks which might occur at junction point 60. Looked at from a different point of view, the switch-over points of the transistor 56 (between blocked and conductive condition) should be as far apart as possible. Referring to FIG. 3, when the temperature T of engine is very low, current will flow through relay 77 indicated as 1),, and by the portion 91 of the graph, and additional fuel will be injected. As the temperature T of engine 10 increases, operation will change to the branch 92 on the graph of FIG. 3, in the direction of the x-axis, until changeover point 93 is reached. At this point, circuit 42 will interrupt the current i through relay coil 77. When the temperature of engine 10 is higher than given by the position of point 93, the current will be zero as indicated by the branch of the curve 94 and no additional fuel is injected, The temperature of the internal combustion engine 10, after operation of ignition switch 52, may be in the region of the branch 95 of the characteristics, that is within the hysteresis loop. No additional fuel would be injected under such conditions and the additional valve 44 would open only when the temperature falls below the point 96 on the operating curve.

Condenser 58 ensures that the initial condition of circuit 42 at all times is the same since, upon closing ignition switch 52, a positive pulse will be passed over condenser 58 to the base of transistor 56, initially and for a short time blocking the transistor 56 regardless of other operating conditions. The circuit, depending on the temperature of the engine 10 (as sensed by resistance 41) will then go through the operating conditions determined by the characteristics of FIG. 3, beginning with the branch of the curve 91. If the temperature is higher than point 93, the hysteresis effect of the circuit will be immaterial.

The base of output transistor 67 is, in accordance with another feature of the invention, interconnected with the base of transistor 66 of the bistable multivibrator over an integrating network formed of resistance 72 and condenser 73, so that noise, and particularly stray noise pulses are suppressed.

It is often difficult to completely eliminate possibilities of misconnection in the electrical equipment of vehicles, particularly during servicing, or if the additional fuel injection system is added as a further option at a later time. It would thus be possible that a controlled semiconductor, for example the final output transistor 67, is connected directly to the battery 50 rather than through relay .77, for example if, by mistake, a direct cable is connected rather than the relay coil. Upon operation of the starting switch, immediate destruction of transistor 67 would result. The final output transistor 67 is therefore protected by an inherent fail-safe circuit which is controlled by the collector-emitter current of transistor 67 to control the transistor 67 in such a way that its resistance increases to limit the current therethrough to a safe value. Sensing resistance 76 is therefore interconnected between the emitter-collector of transistor 67 in series with chassis.

When engine 10 is cold, and starter switch 46 is closed, current will flow from battery 50 over resistance 69 and diode 71 (transistor 66 being blocked) and then over the group of diodes 74 to chassis. Further, current will flow over resistance 69 and diode 71 to the base of transistor 67, causing transistor 67 to become conductive. The value of the resistance 75 is chosen to be high with respect to the base-emitter resistance of transistor 67 so that current flowing therethrough can be neglected. Transistor 67 being conductive, current i will flow from positive terminal of battery 50 over relay coil 77, the switching path (collector-emitter) of transistor 67 and the sensing resistance 76. The value of resistance 76 is chosen to be small, so that under ordinary operating conditions the voltage thereacross will'be small with respect to the voltage across the diode group 74, forming a constant voltage source. Transistor 67 remains conductive. If, however, a short circuit directly to the positive terminal of the battery, for example by an interchange of coil and switch terminals of the relays 77-82, the current through the transistor 67 is limited by the increase in current through resistance 76. In ordinary silicon transistors, the base-emitter voltage drop (forming a diode element) has an approximately constant value of 0.8 V. lf the resistance 76 is so dimensioned that the voltage across resistance 76 will be equal to the difference of the voltage across the diode group 74 and the voltage between base and emitter, the collector current (and with it the current to resistance 76 itself) will drop since the base-emitter voltage will drop, causing a corresponding drop in base current of the transistor 67. This decreases the conduction of transistor 67, until a point is reached in which equilibrium is reached between the collector current and the base current, in view of the amplification factor of transistor 67. Sensing resistance 76 is thus so dimensioned that, even if transistor 67 is connected directly across the battery, the current therethrough will not rise to destructive values. The number of the diodes 74 in the constant voltage source is so chosen that the required base-emitter voltage of about 0.8 V is obtained under ordinary operating conditions.

The present invention therefore provides a circuit in which a temperature sensing element is used to control an additional injection valve, the entire circuit itself, however, being essentially independent of ambient temperature. Thus, additional fuel upon starting is being supplied, the entire unit being capable of separate installations and specifically designed for use under cold-weather condition. The additional fuel is supplied only during starting, the circuit being connected to be ready to supply additional fuel only during the period in which the starting switch is closed. Condenser 58 always brings the circuit in a predetermined condition, ready to supply additional fuel if the temperature is low. Various changes and modifications may be made within the scope of the inventive concept.

We claim:

1. Temperature sensitive control circuit for internal combustion engine fuel injection systems having an electromagnetic control coil controlling operation of a fuel injection valve, adapted for connection to a source of power, comprismg:

a bridge circuit 41, 54, 59, 61 having its end points connectable across said source, one branch of said bridge circuit including a temperature sensitive resistance 41 located in temperature sensing relation to the engine 10;

a diode element 55 and a transistor 56, the base-emitter path of said transistor and said diode element being connected in series and across the center points 60, of the bridge circuit;

a biasing resistance 57 connected to the junction between said diode element and the transistor, and to one terminal of said source, said diode element being poled with respect to the base-emitter path of said transistor to compensate for ambient temperature changes, whereby the emitter-collector conduction of said transistor will be controlled only by said temperature sensitive resistance; and

means interconnecting the emitter-collector path of said transistor and the control coil 77 of the fuel injection valve.

2. Circuit according to claim 1, wherein said diode element is a diode 55 poled opposite to the base-emitter path of said transistor 56.

3. Circuit according to claim 2, wherein said bias resistance and said temperature sensitive resistance are connected in a parallel circuit, said diode forming one of said parallel interconnections and a terminal of the source forming the other parallel interconnection.

4. Circuit according to claim 1, wherein a separate fuel injection valve 44 is provided, located to supply additional fuel to all cylinders of the engine, said interconnection means controlling operation of said additional valve.

5. Circuit according to claim 4, wherein said internal combustion engine has an intake manifold having a common air supply, said additional valve being located in said intake manifold adjacent the inlet of said common air supply to said manifold.

6. Circuit according to claim 1, wherein said internal combustion engine has a starter switch; and said control circuit is connectable to said source through said starter switch whereby additional fuel can be injected only during operation of said starter switch.

7. Circuit according to claim l,- wherein said interconnection means includes an additional transistor 66 in a flip-flop circuit and complementary to said transistor 56 to provide for positive on-off switching.

8. Circuit according to claim 1, wherein said temperature sensitive resistance 41 is a negative temperature coefficient resistance.

9. Circuit according to claim 7, including an output transistor 67 having its conduction controlled by said flip-flop circuit and connected in series with the control coil 77 of said valve:

a sensing resistance in series with the emitter-collector path of said output transistor;

a constant voltage source 74; and

a comparison resistance 75 interconnecting the emitterbase path of the transistor and the constant voltage source and comparing the voltage across said sensing resistance with the constant voltage of said source, said comparison resistance applying an error potential to the base of the output transistor in a direction to decrease its.

conduction when the error potential has a value and direction indicative of excessive current through said transistor.

10. Circuit according to claim 9, wherein the collectoremitter path of the output transistor 67 is connected in a series circuit with the control coil of said valve and to one terminal of said source and connected in a series circuit with said sensing resistance to the other terminal of said source.

11. Circuit according to claim 1, including a condenser 58 interconnecting the junction of said diode element 55 and the transistor 56 with a terminal of the source.

12. Circuit according to claim 1, including a voltage divider having a plurality of resistors 62, 64 connected in parallel to the control coil 77 of the fuel injection valve, at least one of said resistances 62 being common to a branch 61, 62 of said bridge circuit.

13. Circuit according to claim 12, including an output transistor 67 having its conduction controlled by said flip-flop circuit and connected in series with the control coil 77 of said valve, wherein said voltage divider is connected at one end terminal directly to said source, at the other end terminal to the collector of said output transistor 67 and said voltage divider has a tap point connected to a resistance and then to one of the cross terminals 70 of the bridge. 

